ext/pango/gsttextoverlay.*: API: add "line-alignment" property (#459334). Add gtk-doc blurb for "silent" property so ...

Original commit message from CVS:
Patch by: Dan Williams  <dcbw redhat com>
* ext/pango/gsttextoverlay.c:
* ext/pango/gsttextoverlay.h:
API: add "line-alignment" property (#459334). Add gtk-doc blurb for
"silent" property so there's a Since tag in the API reference.